Background: HIV and HIV-related proteins are produced by recombinant DNA methods for high-resolution structural analyses. The proteins are selected which are important for the life cycle of the virus and for its structural integrity and, thus, represent potential targets for rational structure-based drug design. Collaborating groups performed the actual structure determinations. The determination of the 3-D structure of proteins by X-ray diffraction or multidimensional NMR required the production of large quantities of highly purified and physically homogeneous protein. In addition, protein structure determination by NMR requires protein biosynthetically labeled with combinations of the stable isotopes: H-2, C-13 and N-15. Results: (1) Nef is a 23 kDa protein essential for the pathogenic properties of HIV. We are investigating some of the specific protein-protein interactions involving Nef especially interaction with the 39-residue cytoplasmic tail of CD4. We have devised novel expression systems for producing the small CD4 domain that are useful in general for producing small and relatively unstable peptides. To study the interaction using NMR, the Nef protein has been modified to enhance its solubility. This work is still in progress and we are continuing to modify both Nef and CD4 to facilitate the study. (2) HIV Rev is an important regulatory factor required for HIV expression. We have made extensive modifications of the Rev protein in order to improve its solubility for NMR measurements. (3) HIV protease, a homodimeric protein is essential in the viral life cycle and a major anti-AIDS drug target. The modification of residues at the dimer interface result in protease inactivation by interfering with protein-protein association. Summary: the immunodeficiency virus (HIV) comprises a number of proteins with regulatory and structural roles. HIV proteins important for the virus life cycle, and proteins which have anti-HIV activity, are expressed in bacteria using recombinant DNA methods. The proteins are purified then studied to establish their chemical and physical properties. Well-characterized proteins are made available to NIH investigators who study the molecular structure of these proteins. This structural information may provide impetus for targeted drug design and discovery.